Process for deposition of semiconductor films

ABSTRACT

Chemical vapor deposition processes utilize chemical precursors that allow for the deposition of thin films to be conducted at or near the mass transport limited regime. The processes have high deposition rates yet produce more uniform films, both compositionally and in thickness, than films prepared using conventional chemical precursors. In preferred embodiments, a higher order silane is employed to deposit thin films containing silicon that are useful in the semiconductor industry in various applications such as transistor gate electrodes.

RELATED APPLICATION INFORMATION

This application is a divisional of U.S. patent application Ser. No.10/074,563, filed Feb. 11, 2002 now U.S. Pat. No. 6,821,825, whichclaims priority to: U.S. Provisional Application No. 60/268,337, filedFeb. 12, 2001; U.S. Provisional Application No. 60/279,256, filed Mar.27, 2001; U.S. Provisional Application No. 60/311,609, filed Aug. 9,2001; U.S. Provisional Application No. 60/323,649, filed Sep. 19, 2001;U.S. Provisional Application No. 60/332,696, filed Nov. 13, 2001; U.S.Provisional Application No. 60/333,724, filed Nov. 28, 2001; and U.S.Provisional Application No. 60/340,454, filed Dec. 7, 2001; all of whichare hereby incorporated by reference in their entireties. Thisapplication is related to, and incorporates by reference in theirentireties, co-owned and U.S. patent application Ser. No. 10/074,149(now U.S. Pat. No. 6,716,751); Ser. Nos. 10/074,722; 10/074,633;10/074,564; and 10/074,534, all of which were filed on Feb. 11, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to depositing semiconductor films, suchas those containing Si, Ge and/or carbon for integrated circuitfabrication. More particularly, the invention relates to making thesematerials with greater thickness and compositional uniformity inchemical vapor deposition systems.

2. Description of the Related Art

As the dimensions of microelectronic devices become smaller, theimportance of the physical and chemical properties of the materials usedin their manufacture becomes more important. This is particularly truefor those advanced materials that can be integrated into existinggenerations of devices using already-proven manufacturing tools. Forexample, it would be desirable to incorporate epitaxial Si_(1-x)Ge_(x)and Si_(1-x-y)Ge_(x)C_(y) alloys into Bipolar and BiCMOS devicemanufacturing processes. These advanced alloy materials have utility asbase layers in heterojunction bipolar transistors (HBT), resistors inBiCMOS devices and as gate electrodes in CMOS devices and various otherintegrated electronic devices.

Conventional processes for the deposition of single crystal, amorphousand/or polycrystalline silicon, silicon germanium (SiGe) and silicongermanium carbon (SiGeC) alloys are typically performed using batchthermal processes (either low pressure (LP) or ultra-high vacuum (UHV)conditions) or single wafer processes. Single wafer processes arebecoming increasingly significant, but a number of problems remain. Forinstance, within-wafer and wafer-to-wafer uniformity, deposition rates,and process repeatability remain a concern with conventional singlewafer processes, particularly for in situ doped semiconductor films. Aswafers continue to increase in size (currently 300 mm wafers are beingintegrated into fabrication processes), maintaining uniformity isbecoming more challenging still.

Japanese Patent Application Disclosure Number S60-43485 discloses theuse of trisilane to make amorphous thin films at 300° C., apparently forphotovoltaic applications. Japanese Patent Application Disclosure NumberH5-62911 discloses the use of trisilane and germane to make thin filmsat 500° C. or less. Japanese Patent Application Disclosure NumberH3-91239, H3-185817, H3-187215 and HO2-155225 each disclose the use ofdisilane, some also mentioning trisilane.

The art has generally focused on the use of disilane and trisilane forproducing amorphous, hydrogenated silicon at relatively low depositiontemperatures. However, there remains a need for a process for depositingsemiconductor materials such as doped silicon, low-H content amorphoussilicon and SiGe onto surfaces, preferably at high deposition rateswithout sacrificing good uniformity.

SUMMARY OF THE INVENTION

The inventors have discovered better ways of making Si-containing andGe-containing films. Methods are taught for using chemical precursorssuch as higher-order silanes and/or higher-order germanes in CVDprocesses to provide improved deposition of Si-containing films,particularly silicon, SiGe or SiGeC alloy thin films useful in thesemiconductor industry. These chemical precursors have reduced thermalstability relative to silane, germane and conventional carbon-sourcemolecules.

In accordance with one aspect of the invention, the use of particularprecursors allows the deposition process to be conducted closer to, orwithin, a mass transport limited growth regime, relative to conventionalprecursors at the same temperature. Within this regime, temperaturedependent non-uniformities, such as undesirable elemental concentrationgradients and variable film deposition rates, and consequent thicknessnon-uniformities, can be avoided. Preferred chemical precursors includetrisilane and trisilane in combination with digermane. Uniformdeposition can be achieved at temperatures lower than those used forconventional chemical precursors, with higher film deposition rates.

In another aspect of the invention, flow rates of the preferredprecursors are adjusted as a function of temperature to obtain higherdeposition rates with equal or greater uniformity, as compared withdeposition using conventional precursors (e.g., silane). The advantagesof trisilane over silane have been found particularly applicable to thedeposition of silicon-containing layers as active layers in integratedtransistors.

In another aspect of this invention, methods are taught for stepwise ordynamically changing process parameters such as temperature, temperaturedistribution, pressure, reactant flow rate and reactant partial pressurein such a way as to reduce or eliminate such undesirable elementalconcentration gradients, thickness non-uniformities and variable filmdeposition rates. These methods can be used in conjunction with the useof higher order silanes and/or germanes.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be readily apparent fromthe following description and from the appended drawings, which aremeant to illustrate and not to limit the invention, and wherein:

FIG. 1 is a flow chart generally illustrating the process of forming agate stack in accordance with a preferred embodiment;

FIG. 2 illustrates a gate stack in accordance with a preferredembodiment;

FIG. 3 is a flow chart generally illustrating the process of changingthe temperature set point during the deposition process in accordancewith a preferred embodiment;

FIG. 4 shows a plot of film thickness as a function of measurement sitefor a preferred SiGe film;

FIG. 5 is a reproduction of a scanning electron photomicrographillustrating a SiGe film deposited using silane and germane;

FIG. 6 is a reproduction of a scanning electron photomicrographillustrating a cross section of the SiGe film shown in FIG. 5;

FIG. 7 is a reproduction of a scanning electron photomicrograph showinga SiGe film deposited using trisilane and germane;

FIG. 8 is a reproduction of a scanning electron photomicrograph showinga cross section of the SiGe film shown in FIG. 7;

FIG. 9 is a reproduction of a transmission electron photomicrographshowing a cross section of a preferred SiN film;

FIG. 10 shows an Arrhenius plot obtained under the conditions describedbelow for silane, disilane, and trisilane;

FIG. 11 shows a plot illustrating film deposition rate on an oxidesubstrate as a function of trisilane (Silcore™) flow rate at 600° C., 40Torr;

FIG. 12 shows a plot illustrating film thickness as a function ofposition for various deposition times using trisilane (Silcore™) at 650°C., 40 Torr;

FIG. 13 shows a plot of deposition rate as a function of diborane flowfor deposition using trisilane;

FIG. 14 shows a RBS ERD spectrum for an amorphous silicon film depositedusing trisilane at 600° C., 40 Torr;

FIG. 15 shows a series of X-ray diffraction patterns obtained for filmsdeposited using trisilane at 600° C., 650° C., 700° C. and 750° C.(bottom to top, respectively);

FIG. 16 is a reproduction of a transmission electron photomicrograph ofa cross-sectioned polycrystalline silicon film;

FIG. 17 shows a selected area diffraction pattern for a polycrystallinesilicon film;

FIG. 18 is a reproduction of a scanning electron photomicrograph of across-sectioned conformal amorphous silicon film;

FIG. 19 shows a RBS spectrum for a silicon nitride film; and

FIG. 20 shows a RBS ERD spectrum for a silicon nitride film.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Dynamic temperature variations, due to limitations in heating andtemperature control systems, play a significant role in thenon-uniformity of film deposition on substrate surfaces by CVD. It isgenerally desirable for the deposited film to be as uniform as possiblein both thickness and elemental composition, but existing processes tendto produce films that are non-uniform to varying degrees. Suchnon-uniformities often result from temperature variations across thesurface of the substrate because the surface temperature of thesubstrate influences the deposition rate and the composition of theresulting film. Imperfect control over other process parameters,including gas flow rates and total pressure, are also believed tocontribute to non-uniformities in film physical properties.

Uniformity is often sought by empirically tuning the depositionconditions e.g., gas flow rate, rotation speed of substrate, powerdistribution to heating elements, etc., to achieve an overall uniformthickness for the desired film. This is done by first depositing a largenumber of films on different substrates, each under a differentpre-selected set of deposition conditions. The thickness variationswithin each film are then measured and the results analyzed to identifyconditions that would eliminate the thickness variations. The inventorshave realized, however, that this empirical process does not necessarilyachieve uniform temperature distributions throughout the process;rather, the process effectively time-averages the thickness variationsproduced by the temperature variations for a specific reactiontemperature ‘set-point’.

Accordingly, this empirical approach does not necessarily produceuniform temperatures across the substrate throughout the depositionprocess. This, in turn, raises the issue of compositional variationbecause compositional homogeneity (or at least control) is desired inthree dimensions, both across the film surface and through the filmthickness. This is because many films contain dopants and the level ofthese dopants influences the electronic properties of the film.Non-uniform temperatures can result in non-uniform incorporation ofdopants into the film. Similarly, other non-uniformities in compositioncan result.

The preferred embodiments provide processes for solving this problem,each of which may be used individually or, preferably, together. Oneprocess involves the use of chemical precursors that allow for filmdeposition to be conducted substantially within a mass transport limitedgrowth regime, relative to conventional precursors at the sametemperature. For a given chemical precursor, the mass transport limitedregime is a temperature range in which film deposition rates areindependent of temperature. Deposition rates that are substantiallywithin this temperature range are relatively unaffected by smalltemperature variations across the surface of the substrate, so long asthose variations result in temperatures that remain at or near the masstransport limited regime. This allows for the production of films thatare much more uniform, e.g., exhibit higher compositional uniformityand/or thickness uniformity, than films deposited at the sametemperature using conventional chemical precursors. This is becauseconventional precursors require much higher temperatures in order fordeposition to be in the mass transport limited regime.

As will be appreciated by the skilled artisan, the temperature range forthe mass transport limited regime can be determined for a givenprecursor and set of reaction conditions, and illustrated in anArrhenius plot. For the chemical precursor trisilane, the transitionpoint from temperature-dependent deposition rates totemperature-independent deposition rates is much lower than thetransition point for silane or disilane, as illustrated in the Arrheniusplot shown in FIG. 10. The lower region of the plot up to the transitionhas a significant upward linear slope, indicating that deposition oftrisilane within this temperature range is a strong function oftemperature and therefore not within the mass transport limited regime.For example, FIG. 10 shows that trisilane deposition is not masstransport limited (i.e., is within the kinetic regime) at temperaturesless than about 525° C., under the conditions used (25 sccm flow rate,40 Torr pressure). In contrast, the region of the plot above thetransition point is substantially flat, indicating that deposition oftrisilane within this temperature range is independent of temperatureand therefore within the mass transport limited regime. For example,FIG. 10 shows that trisilane deposition is clearly mass transportlimited at temperatures of about 620° C. or greater. It will beunderstood that the transition occurs over a range of temperatures inwhich the declining slope of the Arrhenius plot indicates that thedeposition of trisilane within this temperature range is substantiallyindependent of temperature, near the mass transport limited regime. Forexample, FIG. 10 shows that trisilane deposition is substantially masstransport limited at temperatures of about 525° C. or greater. It willbe understood that the transition point may increase somewhat at higherflow rates, and decrease somewhat at lower flow rates. For example, ithas been determined experimentally that the transition point fromtemperature-dependent deposition to substantially mass transport limiteddeposition shifts to higher temperatures when the trisilane flow rate isincreased. Accordingly, the use of trisilane enables substantially masstransport limited deposition at temperatures that are desirable forother reasons in contemporary fabrication (e.g., conservation of thermalbudgets for maintaining crystal properties, controlling dopant profiles,etc.).

A variety of silicon- and germanium-containing chemical precursors canbe suitably used in the film deposition processes disclosed herein toprovide Si-containing films, Ge-containing films and alloy films thatcontain both Si and Ge, e.g., silicon germanium (SiGe, without implyingstoichiometry) films. These chemical precursors may also be used inconjunction with carbon sources to provide alloy films, e.g., SiGeC(without implying stoichiometry) alloy thin films. PreferredSi-containing chemical precursors suitable for use in the instantinvention include higher-order, non-halogenated hydrides of silicon,particularly silanes of the formula Si_(n)H_(2n+2) where n=2-6.Particular examples include disilane (H₃SiSiH₃), trisilane(H₃SiSiH₂SiH₃), and tetrasilane (H₃SiSiH₂SiH₂SiH₃). Trisilane (alsorepresented by Si₃H₈) is most preferred for achieving a balance ofvolatility and reactivity. Substantially or nearly mass transportlimited deposition, at relatively low temperatures, is preferred (butnot necessary) for SiGe deposition. Preferred Ge-containing chemicalprecursors suitable for use in the instant invention includehigher-order germanes of the formula Ge_(n)H_(2n+2) where n=2-3. Inother arrangements, the germanium source can comprise(H₃Ge)(GeH₂)_(x)(GeH₃), where x=0-2. Particular examples includedigermane (H₃GeGeH₃), trigermane (H₃GeGeH₂GeH₃) and tetragermane(H₃GeGeH₂GeH₂GeH₃).

In a preferred embodiment, the chemical precursors are used inconjunction with a source of carbon. Preferred carbon sources includesilylmethanes [(H₃Si)_(4-x)CR_(x)] where x=0-3 and R=H and/or D. Thepreferred silylmethanes are disilylmethane, trisilylmethane andtetrasilylmethane (x=0-2), with tetrasilylmethane being most preferred.Additional preferred carbon sources include hydrocarbons such asmethane, ethane, propane, butanes, etc.; carbon monoxide, carbon dioxideand HCN. These chemical precursors and carbon sources may be purchasedfrom commercial sources or synthesized by methods known to those skilledin the art. Si-containing films such as SiC, SiNC and SiOC (none ofwhich short forms imply a particular stoichiometry) have a variety ofuses in the semiconductor manufacturing industry, e.g., as etch stoplayers, hard masks, and passivation layers.

The films are preferably deposited at a temperature that issubstantially within the mass transport limited regime for theparticular chemical precursor that is used. For any particular chemicalprecursor and set of reaction conditions, the mass transport limitedregime can be determined from an Arrhenius plot empirically-derived fromdeposition data at various temperatures. The Arrhenius plot for the mostpreferred silicon precursor, trisilane, for a particular set ofconditions is appended as FIG. 10, discussed above.

In addition to employing preferred chemical precursors (particularlytrisilane) as described herein and selecting a deposition temperaturewithin the mass transport limited regime for that precursor, depositionusing the first process preferably involves proper selection of otherdeposition parameters, particularly gas flow rate. Proper selection ofgas flow rate, in combination with deposition substantially within themass transport limited regime, has been found to yield films at muchhigher deposition rates compared to silane, while maintaining a highdegree of uniformity. For depositions using silane at temperatures inthe kinetic regime, film uniformity depends primarily on the temperaturecontroller set points and, to a much lesser extent, the gas flow ratecontroller set points. In contrast, for depositions involvinghigher-order silanes at temperatures substantially within the masstransport limited regime, it has been found that the sensitivity totemperature controller set points and gas flow controller set points isreversed. For example, for depositions using trisilane at temperaturessubstantially within the mass transport limited regime, tuning thetemperature controller set points has much less effect on filmuniformity than tuning the gas flow rate controller set points.

When deposition is conducted as described herein, the resulting film ispreferably more uniform than a comparable film. As used herein, a“comparable” film is made in a manner that is substantially identical inall meaningful aspects to the inventive film in question, except thatsilane is used in place of a higher-order silane and/or germane is usedin place of a higher-order germane, and the deposition process for eachfilm is individually tuned to take into account the aforementioneddifferences in sensitivity to temperature and gas flow controller setpoints. More particularly, when comparing the results of differentlayers, thickness uniformity is to be measured by the followingstandard: a randomly selected diameter across a wafer is employed and 49points along that diameter are measured for deposited layer thickness.No measurements are taken within a 3 mm exclusion zone at the waferperiphery. The range in thickness measurements (e.g., ±6 Å) over those49 points is then divided by the sum of the maximum thicknessmeasurement plus the minimum thickness measurement from among the 49points. This non-uniformity is expressed as a percentage herein. Whenmeasuring thickness uniformity of a film having a surface that is notaccessible to such a measurement, e.g., a film onto which one or moreadditional layers have been applied, or a film contained within anintegrated circuit, the film is cross sectioned and examined by electronmicroscopy. The film thickness is measured at the thinnest part of thecross sectioned film and at the thickest part, and the range inthickness measurements (e.g., ±6 Å) between these two points is thendivided by the sum of the two measurements. This non-uniformity isexpressed as a percentage herein. Advantageously, the methods employingthe precursors described herein have been found to result inextraordinarily high deposition rates and yet, surprisingly, obtainexceptionally high uniformity and smoothness.

For example, a preferred polycrystalline silicon film is made usingtrisilane and has greater uniformity at greater deposition rates than acomparable film made from a process separately optimized using silane inplace of said trisilane at the same temperature. Similarly, theinventors have separately experimented with and found amorphous silicon(α-Si) layers and epitaxial silicon (epi-Si) layers formed withtrisilane to exhibit better uniformity as compared with silane-depositedlayers. See FIGS. 15-18 and corresponding text hereinbelow. Likewise, apreferred SiGe film is made using a higher order germane and has greateruniformity than a comparable film made using germane in place of saidhigher-order germane. Furthermore, higher deposition rates at a lowerreaction temperature are also attainable using the silicon and germaniumsources disclosed.

FIG. 11 shows that deposition rate is a linear function of the trisilane(referred to as “Silcore™” in some of the figures) flow rate at adeposition temperature of 600° C. and a pressure of 40 Torr. Thislinearity is a further indication that trisilane deposition issubstantially or nearly mass transport limited under these conditionsand further indicates very low nucleation times over oxide. FIG. 12 is aplot of film thickness as a function of measurement site for filmsdeposited using trisilane under identical conditions (650° C., 40 torr),except that the deposition time was varied over a range from 90 secondsto 15 seconds as indicated. FIG. 12 shows that, at a fixed trisilaneflow rate, exceptional film uniformity is obtained for a wide range ofdeposition times, indicating that the results are not merelytime-averaged but result from the nature of the precursor and selectedconditions, and further that emissivity (or other thickness-dependenttemperature control) effects do not alter the uniformity, since thelayers remain uniform regardless of thickness. FIG. 13 is a plot of thedeposition rates obtained using trisilane and diborane (a dopantprecursor) at a deposition temperature of 600° C. and a pressure of 40Torr, over a range of diborane flow rates (zero to 180 sccm). FIG. 13shows that deposition rates using trisilane are relatively insensitiveto the flow rate of the dopant precursor.

The preferred temperature range tends to depend on the particularchemical precursor, with lower temperatures being more appropriate asthe thermal stability decreases. For higher-order silanes and higherorder germanes, lower temperatures are preferred as chain-lengthincreases. Thus, the preferred temperature range for disilane depositiontends to be higher than for trisilane, which in turn tends to be higherthan for tetrasilane, etc. A similar trend holds for the germane series.A preferred temperature for depositing trisilane is higher than about350° C., preferably higher than about 450° C. in order to minimizehydrogen content in the resulting film. More preferably, in order toattain deposition near or within the mass transport limited regime,temperatures are maintained higher than about 525° C., even morepreferably higher than about 550° C., most preferably higher than about600° C. The process may be carried out at a temperature above 700° C.,but a temperature of about 700° C. or less is preferred. Preferredtemperatures are thus in the range of 450° C. to about 700° C., morepreferably in the range from about 525° C. to about 650° C. For anyparticular chemical precursor or mixture thereof, the most preferredtemperature range may be found through routine experimentation,following the guidelines provided herein. It will be understood that thelisted temperatures are preferred for thermal CVD. Lower temperatureswill be appropriate for plasma assisted deposition processes, dependingupon the level of hydrogen incorporation that is acceptable for theapplication.

Selection of the deposition temperature can also depend partly upon thedesired crystallinity in the layer being deposited. For example,predominantly crystalline silicon can be deposited in the range of about620° C. to 800° C., which is clearly within the mass transport limitedregime, as discussed above. More preferably, polysilicon deposition isconducted between 650° C. and 750° C. Lower temperatures can be used foramorphous silicon deposition, but preferably temperatures are selectedto remain at least substantially mass transport limited (i.e.,preferably at higher than 525° C. for the preferred conditions).Epitaxial silicon is largely dependent upon the purity of the surfaceupon which deposition is to take place. Namely, as will be recognized bythe skilled artisan, an extremely clean single-crystal surface, such asthe upper surface of a previously-deposited epitaxial layer or the uppersurface of a single crystal wafer, enables epitaxial deposition at alarge range of temperatures, depending upon flow rates, pressure, etc.Typically, epitaxial deposition upon a suitable surface can take placebetween 500° C. and 1160° C. It is preferred to employ the lowertemperature ranges, such as from about 500° C. to about 750° C., forreasons of consideration of thermal budgets. See FIGS. 15-18 andcorresponding text hereinbelow.

Preferably, deposition is carried out using a chemical precursor e.g.,higher-order silane and/or higher-order germane, at a temperature thatis effective to achieve higher deposition rates and/or more uniformfilms, as compared to comparable films made using silane and/or germane.

Deposition of these chemical precursors may be suitably conductedaccording to the various vapor deposition methods known to those skilledin the art, but the greatest benefits are obtained when deposition isconducted according to the improved chemical vapor deposition (CVD)process techniques taught herein. The disclosed processes may besuitably practiced by employing CVD, including plasma-enhanced chemicalvapor deposition (PECVD) or thermal CVD, utilizing a feed gas comprisedof a Si- and/or Ge-containing chemical precursor to deposit a Si- and/orGe-containing film onto a substrate contained within the CVD chamber. Ina preferred embodiment, the gas is comprised of trisilane and aSi-containing film is deposited. In another preferred embodiment, thegas is comprised of a higher-order silane and a higher-order germane,and a SiGe film is deposited.

A suitable manifold may be used to supply feed gas(es) to the CVDchamber. Experimental results described herein were conducted in a CVDchamber with horizontal gas flow, and preferably the chamber is asingle-wafer, horizontal gas flow reactor, preferably radiativelyheated. Suitable reactors of this type are commercially available, andpreferred models include the Epsilon™ series of single wafer epitaxialreactors commercially available from ASM America, Inc. of Phoenix, Ariz.While the processes described herein can also be employed in alternativereactors, such as a showerhead arrangement, benefits in increaseduniformity and deposition rates have been found particularly effectivein the horizontal, single-pass, laminar gas flow arrangement of theEpsilon™ chambers.

The chemical precursors are preferably supplied to the CVD chamber inthe form of a feed gas or as components of a feed gas, at thetemperatures and pressures used for deposition. The total pressure inthe CVD chamber is preferably in the range of about 0.001 Torr to about700 Torr, more preferably in the range of about 0.1 Torr to about 200Torr, most preferably in the range of about 1 Torr to about 60 Torr. Thepartial pressure of each Si- and/or Ge-containing chemical precursor ispreferably in the range of about 1×10⁻⁶% to about 100% of the totalpressure, more preferably about 1×10⁻⁴% to about 100%, same basis. Atmuch lower pressures than 1 Torr (as is typical for batch LPCVDprocesses), high conformality can be achieved, but it is difficult tonucleate continuous layers. On the other hand, at much higher pressureranges (e.g., atmospheric), it has been found that nucleation alsoappears to be less rapid. The preferred ranges achieve a fine balance oftemperature control insensitivity to patterned wafers and attendantemissivity effects, while obtaining very fast nucleation over oxides,particularly using trisilane. Surprisingly, conformality remainsexcellent at the preferred pressure ranges using trisilane for CVD,despite much higher pressures than those employed in LPCVD processes.The partial pressure of each carbon source, if any, is preferably in therange from 0% to about 1% of the total pressure, more preferably about1×10⁻⁶% to about 0.1%, same basis. If used, the partial pressure of thecarbon source is preferably effective to provide the resultingSi-containing and/or Ge-containing film with a carbon content of about20% or less (10% or less for single crystal materials), even morepreferably about 10% or less (5% or less for single crystal materials),where the percentages are by weight based on total film weight.

The feed gas can also include gases other than chemical precursor(s) andcarbon sources, such as inert carrier gases. Exemplary carrier gasesinclude helium, argon, krypton and neon. Hydrogen is most preferred as acarrier gas for the processes described herein, particularly for singlecrystal materials. Nitrogen can also be employed for polycrystalline andamorphous film deposition. Other compounds can be present in the feedgas as desired. Preferably the gas is further comprised of one or morecompounds selected from the group consisting of silane, disilane,tetrasilane, germane, digermane, trigermane, NF₃, monosilylmethane,disilylmethane, trisilylmethane, tetrasilylmethane, and a dopantprecursor.

Dopant precursors include diborane, deuterated diborane, phosphine, andarsine. Silylphosphines [(H₃Si)_(3-x)PR_(x)] and silylarsines[(H₃Si)_(3-x)AsR_(x)] where x=0-2 and R_(x)=H and/or D are preferreddopant sources of phosphorous and arsenic. SbH₃ and trimethylindium arepreferred sources of antimony and indium, respectively. Such dopants anddopant sources are useful for the preparation of preferred films such asboron-, phosphorous-, antimony-, indium-, and arsenic-doped silicon,SiGe and SiGeC films, by the methods described herein. The dopantconcentration in these materials, when doped, is preferably in the rangeof from about 1×10¹⁴ to about 1×10²² atoms/cm³. Dopants can beincorporated using very low concentrations of the dopant sources, e.g.,as mixtures in hydrogen with concentration ranging from about 1 ppm toabout 1%, by weight based on total. These diluted mixtures can then bedelivered to the reactor via a mass flow controller with set pointsranging from 10 to 200 standard cubic centimeters per minute (sccm),depending on desired dopant concentration and dopant gas concentration.The dopant source is also preferably further diluted in the carrier gasdelivered to the reactor with the silicon/germanium/carbon sources.Since typical flow rates often range from about 20 standard liters perminute (SLM) to about 180 SLM, the concentration of the dopant used in atypical process is typically very small.

The relative partial pressures of the chemical precursors (and carbonsource, if any) can be held relatively constant over the course ofdepositing the Si-containing and/or Ge-containing film, or can be variedto produce a graded film that has differing amounts of Si and/or Ge as afunction of depth within the thickness of the film. Preferably, the filmhas a thickness in the range of about 10 Å to about 5,000 Å. Theelemental composition of the film may vary in a stepwise and/orcontinuous fashion. Film thickness may be varied according to theintended application as known in the art, by varying the deposition timeand/or gas flow rates. Whether constant or graded, compound and dopedfilms deposited by the methods described herein have relatively constantcomposition across a plane at any particular given depth. The “plane” inthis sense may undulate if the film is deposited over a patternedsubstrate.

Deposition of the films described herein is preferably conducted at arate of about 50 Å per minute or higher, more preferably about 75 Å perminute or higher, most preferably about 100 Å per minute or higher. Theresulting Si-containing film is preferably selected from the groupconsisting of a SiGe film, a SiGeC film, a silicon nitride film (SiN,without implying stoichiometry), a silicon oxide film (SiO, withoutimplying stoichiometry), a silicon oxynitride film (SiON, withoutimplying stoichiometry), a boron-doped film, an arsenic-doped film, aphosphorous-doped film, and a film having a dielectric constant of about2.2 or lower. Methods for making suitable low-k films are disclosed inco-pending and co-owned U.S. application Ser. No. 09/993,024, filed Nov.13, 2001, the disclosure of which is incorporated herein by reference.The Si-containing film can be amorphous, polycrystalline or epitaxial.Trisilane has been shown to be particularly advantageous for improvingdeposition rates and uniformity of epitaxial silicon layers.

The preferred embodiments also provide another process for solving theuniformity problems discussed above. Examples of this process are givenin FIG. 3 and Example 39, and the process is described more generallyhere. Through-thickness compositional non-uniformities in depositedfilms are believed to result from, inter alia, dynamic (as opposed tostatic) variations in substrate surface temperature. CVD chambers aregenerally equipped with a temperature controller that is configured toallow programming with a set of temperature control conditions that arekept constant throughout the deposition of a particular layer. This setpoint temperature is generally selected at the beginning of the processand maintained until the layer is completed. As discussed above, thethickness problem was approached in the past by empirically tuning thedeposition conditions e.g., gas flow rate, rotation speed of substrate,power distribution to heating elements, etc., to effectivelytime-average the thickness effects of the temperature variations.

It has been found that a temperature set point, or a set of reactorconditions affecting temperature control more generally, that results ina film that is relatively uniform in composition and thickness for thefirst 5 Å to 1,000 Å of film deposition can be found empirically, butthe film then typically becomes less uniform as deposition continues.The reasons for this are not well understood, and this invention is notlimited by theory, but emissivity and other properties of the substrate,that change as a function of deposition time, can affect the temperaturecontrol system. This, in turn, can produce temperature variations thatresult in compositional and thickness variations.

Whatever the reason for the shift to less uniform deposition, it has nowbeen found that a layer-by-layer approach can be used to produce filmshaving greater uniformity. In accordance with this embodiment, a set ofempirically-determined temperature set points T₁, T₂, T₃, etc. can bedetermined on a layer-by-layer basis. A single film, having a singlefunction at a particular point in an integrated circuit, is broken downinto several layers during the empirical determination and optimal setpoints are determined for each layer. Accordingly, temperature controlvariations caused by the growing thickness of the film can becompensated by use of separately optimized set points during thedeposition process.

Such an empirical determination can be conducted by first depositing afirst layer on each of a number of separate workpieces using varioustemperature set points, then measuring the thickness and compositionalvariation of the first layer on each workpiece to identify which setpoint resulted in the most uniform layer. The target thickness of thelayer may vary as desired, e.g., from about 50 Å to about 1,000 Å,preferably about 100 Å to about 700 Å, depending on the level ofuniformity required for the particular application.

A first layer is then prepared on several more workpieces at theidentified set point T₁ to serve as substrates for the empiricaldetermination of the second set point T₂. As in the determination of T₁,a second layer is deposited onto the first film of each of theseworkpieces using various temperature set points, then the thickness andcompositional variation of each layer is measured to identify whichsecond set point resulted in the most uniform second layer. As above,the target thickness of the second layer may vary as desired, e.g., fromabout 50 Å to about 1,000 Å, preferably about 100 Å to about 700 Å,depending on the level of uniformity required for the particularapplication. The process can then be halted, if the optimized first andsecond layers form a multi-layer film having the desired thickness anddegree of uniformity. If a thicker film is desired, the process can becontinued by, e.g., preparing a batch of workpieces having two layersdeposited at the first two identified set points T₁ and T₂, depositing athird layer onto the second layer of each workpiece using varioustemperature set points, measuring the thickness and compositionalvariation of each layer to identify which third set point T₃ resulted inthe most uniform third layer, etc.

Temperature set point is used herein as an example of a temperaturecontrol variable that is normally kept constant during a depositionprocess, but that can be varied during deposition by the empiricalprocess taught above. This empirical process can also be applied toother temperature control variables that are normally kept constantduring a single film deposition process, such as temperature offsets fora PID controller or PID coefficient(s).

Process variables such as gas flow rate, gas flow distribution, partialpressure and gas composition are preferably varied in processes similarto that described above for identifying the temperature set point, orduring the same experiments, in order to identify the desired depositionconditions for each layer. Preferably, experimental design methods areused to determine the effect of the various process variables andcombinations thereof on uniformity and/or deposition rate. Experimentaldesign methods per se are well-known, see e.g., Douglas C. Montgomery,“Design and Analysis of Experiments,” 2^(nd) Ed., John Wiley and Sons,1984. For a particular process, after the effect of the various processvariables and combinations thereof on layer uniformity and/or depositionrate has been determined by these experimental design methods, theprocess is preferably automated by computer control to ensure batch-tobatch or wafer-to-wafer consistency. Most preferably, the processimprovements result from in-situ, stepwise or dynamic adjustments to theprocess variables mentioned above. This empirical method of tuningprocess variables to individually improve the properties of the layershas been found to improve the properties of the overall singlestructural or functional film (comprising multiple layers from a processstandpoint) regardless of any theory expressed herein. Therefore, thefunctioning of this embodiment does not depend on the correctness orincorrectness of any theory.

Having determined the desired set points T₁, T₂, T₃, T₄, etc., thepreferred embodiment may be practiced using a CVD chamber that isequipped with a temperature controller configured to allow programmingwith multiple temperature set points for a single recipe. The process ispreferably conducted by entering a temperature set point T, into atemperature controller and introducing a first gas comprised of X₁% of afirst Si-containing chemical precursor to the CVD chamber; where X₁ isin the range of about 0 to about 100. A first Si-containing layer isthen deposited onto a substrate contained within the chamber. Theprocess is preferably continued by entering a temperature set point T₂into the temperature controller, introducing a second gas comprised ofX₂% of a second Si-containing chemical precursor to the CVD chamber, anddepositing a second Si-containing layer onto the first Si-containinglayer, thereby forming a multi-layer Si-containing film. The secondSi-containing chemical precursor may be chemically identical to thefirst Si-containing chemical precursor or may be different, as discussedbelow and illustrated by FIG. 3 and Example 39.

The process can be continued further by, e.g., entering a temperatureset point T₃ into the temperature controller, introducing a third gascomprised of X₃% of a third Si-containing chemical precursor to the CVDchamber, and depositing a third Si-containing layer onto the secondSi-containing layer, and so on, producing as many layers as desired.

Preferred Si-containing chemical precursors include higher order silanesas described elsewhere herein, as well as conventional chemicalprecursors such as silane. Preferably at least one of the firstSi-containing chemical precursor and the second Si-containing chemicalprecursor is selected from the group consisting of silane, disilane andtrisilane. At least one of the first gas, second gas and third gas ispreferably comprised of a compound selected from the group consisting ofgermane, digermane, trigermane, NF₃, monosilylmethane, disilylmethane,trisilylmethane, tetrasilylmethane, and a dopant precursor, as describedelsewhere herein. Preferably, the amount of each Si-containing chemicalprecursor X_(n), for X₁%, X₂%, X₃%, X₄%, etc., in the gas isindependently in the range of about 1×10⁻⁶% to about 100%, preferablyabout 1×10⁻⁴% to about 100%, by volume based on total volume, at anyparticular stage of the deposition process.

The substrate preferably has a temperature of about 350° C. or higher,more preferably in the range of 450° C. to about 700° C. The CVD chamberis preferably a single-wafer, horizontal gas flow reactor. The resultingmultiple layer Si-containing film is preferably selected from the groupconsisting of a microdot, a SiGe film, a SiGeC film, a SiN film, asilicon-oxygen film, a silicon-oxygen-nitrogen film, a boron-doped film,an arsenic-doped film, a phosphorous-doped film, and a film having adielectric constant of about 2.2 or lower. Methods for making suitablelow-k films are disclosed in co-pending and co-owned U.S. applicationSer. No. 09/993,024, filed Nov. 13, 2001, the disclosure of which isincorporated herein by reference.

The processes of the preferred embodiments may be practiced bydepositing the multiple layers of the film in a stepwise or continuousfashion. Advantageously, when the deposition is paused to adjust thetemperature set point, process variables such as flow rate, partialpressure and gas composition can also be adjusted as desired to producefilms having various compositions. For instance, the deposited film mayhave a homogenous or uniform composition as discussed above, or may varyin composition step-wise or continuously. The identity of theSi-containing chemical precursor can be altered during the pause, and/orthe amount in the gas X₁%, X₂%, X₃%, X₄%, etc. can be varied. In apreferred embodiment, the process involves the growth of a gradedgermanium concentration layer by non-continuous or step-wise changes ingermanium concentration, preferably achieved by preparing a superlatticewith discontinuous periodicity by depositing layers of selectedgermanium concentration on top of each other. Example 39, in conjunctionwith Example 43 below, illustrates this embodiment.

It will be understood that the overall “film” of this embodimentconstitutes a single structural film from the point of view of itsfunction in an integrated circuit, and will typically have a similarcomposition throughout its thickness. Similar composition, for defininga single film formed by the stepwise deposition process described above,thus encompasses graded films wherein the same constituents havedifferent concentrations at different points through the thickness ofthe film.

Methods of determining film uniformity and deposition rates are wellknown. Deposition rates may be determined by measuring the averagethickness of the film as a function of time and can be expressed inunits of angstroms per minute (Å/min.). Preferred deposition rates areabout 20 Å/min. or greater, more preferably about 50 Å/min. or greater,most preferably 100 Å/min. or greater. Suitable methods for measuringfilm thickness include multiple-point ellipsometric methods. Instrumentsfor measuring film thickness are well known and commercially availableand preferred instruments include the NanoSpec® series of instrumentsfrom Nanometrics, Inc., Sunnyvale, Calif.

The term “uniformity,” as used herein to refer to the uniformity ofdeposited films, is used to refer to both thickness uniformity andcompositional uniformity. Film thickness uniformity is preferablydetermined by making multiple-point thickness measurements, determiningthe mean thickness, and determining the average amount that the multiplemeasurements differ from the mean. To enable comparisons, the result canbe expressed as percent non-uniformity. Preferably, the percentnon-uniformity is about 10% or less, more preferably about 5% or less,most preferably about 2% or less. Compositional uniformity may bedetermined using electrical measurements (i.e. 4-point probe), SIMS(Secondary Ion Mass Spectrometry), RBS (Rutherford BackscatteringSpectroscopy), Spectroscopic Ellipsometry and/or high resolution X-raydiffractometry (HR-XRD).

When comparing one Si-containing film to another, or one depositionprocess to another, compositional uniformity is measured using SIMSacross a circular wafer substrate onto which the Si-containing has beendeposited. SIMS measurements are made at three locations: one at thecenter of the wafer, one at a point midway between the center and theedge (“r/2”), and one at a point 3 millimeters from the edge (“3 mm edgeexclusion”). For each non-silicon element in question, the amount ofthat element at each location is then determined from the SIMS data, andthe resulting value expressed in atomic % based on total. The threevalues are then averaged, and the standard deviation determined.

For a given Si-containing film or deposition process, compositionalnon-uniformity is the standard deviation divided by the sum of themaximum and minimum measured values, and the result expressed as apercentage. For example, if the three values are 3 atomic %, 5 atomic %,and 10 atomic %, the compositional non-uniformity is 28% because the sumof the minimum and maximum values is 13 and the standard deviation is3.6 (3.6/13=28%). Preferred values of compositional non-uniformity vary,depending on the amount of the element in the Si-containing film. If theamount of element is 1 atomic % or greater, the compositionalnon-uniformity for the Si-containing film is preferably about 25% orless, more preferably about 20% or less, even more preferably about 15%or less, most preferably about 10% or less. Ge content in SiGe films,for example, will typically represent greater than about 1 atomic % ofsuch films, such that the above preferences apply to SiGe films. If theamount of element is in the range of 0.001 atomic percent up to 1 atomic%, the compositional non-uniformity for the Si-containing film ispreferably about 100% or less, more preferably about 75% or less, evenmore preferably about 50% or less, most preferably about 25% or less. Ifthe amount of element is below 0.001 atomic percent, the compositionalnon-uniformity for the Si-containing film is preferably in the range ofabout 400% or less, more preferably about 300% or less, even morepreferably about 200% or less, most preferably about 100% or less. Gecontent in graded SiGe films, for example, may vary over a broad range,and thus more than one of the above ranges may apply depending on theprofile.

FIG. 14 is a Rutherford Backscattering spectrum (elastic recoildetection, ERD) of an amorphous silicon film deposited using trisilaneat a deposition rate of 1306 Å per minute and a pressure of 40 Torr, ata deposition temperature of 600° C. The solid lines are the raw datafrom the film and the dashed line is a model generated from the datasimulation software RUMP™ for an assumed residual hydrogen concentrationof 0.5 at. %. The raw data indicate slight surface contamination,possibly due to absorbed hydrocarbons and/or moisture, but the spectrumindicates that the residual hydrogen concentration within the film isbelow detection limits, corresponding to a hydrogen concentration ofless than 0.2 atomic %.

FIG. 15 shows X-ray diffraction spectra for a series of silicon filmsdeposited using trisilane at deposition temperatures of 600° C., 650°C., 700° C. and 750° C. (bottom to top of FIG. 15, respectively). TheX-ray diffraction patterns show that the film deposited at 600° C. wasamorphous, the film deposited at 650° C. was partially crystalline, andthat the films deposited at 700° C. and 750° C. were increasingly morecrystalline. FIG. 16 shows a reproduction of a transmission electronphotomicrograph of a cross section of the film deposited at 750° C.(middle layer), showing that it has a relatively high degree of filmthickness uniformity, despite thinness, in a polycrystalline filmdeposited using trisilane. A selected area diffraction (SAD) pattern ofthe film (FIG. 17) shows no preferential orientation within the film,indicating that it was polycrystalline.

FIG. 18 shows a reproduction of a scanning electron photomicrograph of across section of an amorphous silicon film deposited using trisilane at600° C. and 40 Torr. The film was deposited onto a curved substrate andshows excellent conformality even into deep, narrow seams.

In another embodiment, higher-order silanes may also be employed for theCVD synthesis, preferably low temperature, low pressure CVD, of siliconnitride (SiN) materials with compositions ranging from almost puresilicon to Si₃N₄. Preferred nitrogen sources include chemical precursorssuch as (H₃Si)₃N (trisilylamine), ammonia, atomic nitrogen, and NF₃.Atomic nitrogen is preferably generated using a remote microwave radicalgenerator. The relative amounts of nitrogen source and higher-ordersilane introduced to the CVD chamber are preferably selected to providethe resulting SiN film with a greater degree of uniformity than acomparable film made using silane in place of the higher-order silane.In a preferred embodiment, atomic nitrogen is introduced continuously,and trisilane is introduced either continuously or in pulses, preferablyin one or more pulses. It has been found that greater film uniformitycan be obtained by introducing the higher-order silane in pulses, andthat extremely thin, highly uniform SiN films can be obtained byintermittent CVD, as demonstrated in the Examples below. Preferred SiNfilms prepared in accordance with this embodiment have a thickness inthe range of about 10 Å to about 300 Å, more preferably about 15 Å toabout 150 Å.

The use of these nitrogen sources as chemical precursors in conjunctionwith trisilane, especially at low temperatures, enables the depositionof SiN materials with a minimal number of N—H bonds in the thin film atdeposition rates much higher than those afforded by processes whichemploy traditional Si sources such as silane. Similar results can befound with other higher-order silanes. For deposition temperatures inexcess of 450° C., hydrogen content is preferably less than 4 atomic %,more preferably less than about 2 atomic % and most preferably less thanabout 1 atomic %. Preferably, deposition is conducted in the masstransport limited regime, as discussed above.

In another embodiment, higher-order silanes may also be employed for theCVD synthesis, preferably low temperature, low pressure CVD, of siliconoxide materials and silicon oxynitride materials. The lowtemperature/high growth rate advantages of higher-order silanes,especially under low pressure CVD conditions, provide a manufacturingadvantage over processes based upon silane. The oxygen source(s) caninclude ozone, oxygen, water, nitric oxide, nitrous oxide, hydrogenperoxide and the like. The nitrogen sources for the introduction ofnitrogen into these materials include trisilylamine, atomic nitrogen,ammonia, and NF₃ (as described above). Such oxygen and nitrogen sourcescan be employed continuously or in discrete steps or in a methodinvolving a combination of these processes. Preferably, deposition isconducted in at least the nearly mass transport limited regime, asdiscussed above. Deposition using trisilylamine and trisilane ispreferably conducted in the range of about 350° C. to about 750° C.,more preferably about 400° C. to about 700° C., most preferably about450° C. to about 650° C. Deposition using NF₃ and trisilane ispreferably conducted in the range of about 300° C. to about 750° C.;more preferably about 350° C. to about 700° C., most preferably about400° C. to about 650° C.

While separate examples are not given, for the deposition of oxides andoxynitrides, the skilled artisan will readily appreciate that theprinciples disclosed herein and as described above for silicon nitrideand silicon germanium compound layers are equally applicable to siliconoxide deposition. Similarly, the advantages of trisilane with respect tolower activation energies and lower temperatures for achieving masstransport limited deposition have value for vapor deposition, andparticularly chemical vapor deposition, of various silicon compoundmaterials.

A preferred embodiment provides films useful in the microelectronicindustry for various applications. A preferred Si-containing film has athickness non-uniformity of less than about 2% and a compositionalnon-uniformity as described above, with respect to different proportionsof elements in the film. Films such as described herein are useful invarious applications, e.g., as a transistor gate electrode. The layersdescribed herein are particularly useful for forming critical devicelayers in integrated circuits, such as gate layers in integratedtransistors. Other examples include semiconductor layers inheterojunction bipolar transistors (HBT's). Processes for making suchintegrated circuits from such films are known to those skilled in theart. These integrated circuits may be incorporated into computer systemsby methods known to those skilled in the art and thus a furtherpreferred embodiment provides a computer system comprised of one or moreof such integrated circuits.

FIG. 1 is a flow diagram showing a preferred process flow in whichdeposition processes described herein can be employed. A gate dielectricis formed 100 over a semiconductor substrate. The gate dielectric iscleaned 110, if necessary, and a silicon-containing layer is deposited120, as described herein, preferably including flowing trisilane. Anoptional further metal layer can also be deposited 130 over theSi-containing, if desired for improved lateral signal transmission.These multiple layers are then photolithographically patterned 140, andfabrication continues 150.

FIG. 2 illustrates a gate stack 200 formed by the process of FIG. 1. Agate dielectric 210 is formed over a semiconductor substrate 220. Anelectrically doped Si-containing film 230 is formed over the gatedielectric 210 and an optional metal layer 240 is positioned over theSi-containing film 230 to form the gate stack 200. The stack 200 is thenpatterned to form gate electrodes (not shown in FIG. 2) and thefabrication of the integrated circuit is continued.

Desirably, the gate dielectric 210 comprises at least one high kmaterial, with a dielectric constant greater than 5 and more preferablygreater than 10. Exemplary materials comprise aluminum oxide, hafniumoxide and zirconium oxide, preferably formed by atomic layer deposition(ALD) for high quality, pinhole free layers. Advantageously, the use oftrisilane at or near the mass transport limited regime, particularly inconjunction with a higher-order germane, compensates for slow nucleationtimes of traditional silicon deposition over such high k materials.

In another example, epitaxial Si-containing layers are deposited,flowing trisilane, over single-crystal substrates. Silicon layers andheteroepitaxial SiGe, SiC and SiGeC layers can be deposited by processesdescribed herein.

Another preferred embodiment provides an apparatus for depositing aSi-containing material on a surface. This apparatus comprises a CVDchamber, a vessel containing trisilane, a feed line operativelyconnecting the vessel to the CVD chamber to allow passage of thetrisilane from the vessel to the CVD chamber, and a temperaturecontroller operatively disposed about said vessel and maintained at atemperature in the range of about 10° C. to about 70° C., preferably 15°C. to about 52° C., to thereby control the vaporization rate of thetrisilane. Examples of suitable temperature controllers includethermoelectric controllers and/or liquid-filled jackets. Preferably, theCVD chamber is a single-wafer, horizontal gas flow reactor. Preferably,the apparatus is also comprised of a manifold operatively connected tothe feed line to control the passage of the trisilane from the vessel tothe chemical vapor deposition chamber. Preferably, a heat source isoperatively disposed about the feed line and the gas lines are heated toabout 35° C. to about 70° C., more preferably between about 40° C. and52° C., to prevent condensation at high gas flow rates. Preferably,trisilane is introduced by way of a bubbler used with a carrier gas toentrain trisilane vapor, more preferably a temperature-controlledbubbler, most preferably a temperature-controlled bubbler in combinationwith heated gas lines to deliver trisilane.

EXAMPLES

The following examples were conducted using an ASM Epsilon 2000™horizontal flow epitaxial reactor system, configured with a Bernoulliwand wafer transfer system, purge-only load locks, a non-slide concavesusceptor, a ‘square’ pre-heat ring, adjustable spot lamps andindependently tunable gas inlet injectors. The Si-containing andGe-containing precursors were supplied to the chamber in a feed gas thatalso contained hydrogen and a diborane dopant. About 120 sccm of 1% B₂H₆in H₂ was diluted in 2 slm H₂ and 120 sccm of this mixture wasintroduced into the reactor, mixed with 20 slm H₂ and the precursor, anddeposited onto a rotating substrate under the flow rate conditions asshown in the examples. Deposition rates were estimated from oxygen andboron depth profiles using SIMS measurements and optical ellipsometermeasurements (Nanometrics).

Examples 1-4

Si-containing films were deposited using trisilane as chemical precursoraccording to the parameters shown in Table 1. The deposition temperaturewas 700° C., well within the mass transport limited regime fortrisilane. However, the resulting films were not uniform and instead hada concave deposition profile (thin in middle and thicker at edges)because the flow rate was inadequate (under these particular depositionconditions) to provide a uniform film.

TABLE 1 Flow Rate Temp. Pressure Set Point Deposition No. (° C.) (Torr)(sccm) Precursor Substrate Profile 1 700 40 50 Si₃H₈ SiO₂ Concave 2 70040 45 Si₃H₈ SiO₂ Concave 3 700 40 15 Si₃H₈ SiO₂ Concave 4 700 40 25Si₃H₈ SiO₂ Concave

Examples 5-15

Si-containing amorphous films were deposited using trisilane and silaneas chemical precursors and diborane as a dopant according to theparameters shown in Table 1. About 120 sccm of 1% B₂H₆ in H₂ was dilutedin 2 slm H₂ and 120 sccm of this mixture was introduced into the reactorwhere it was mixed with 20 slm H₂ and trisilane or silane at the flowrate shown in Table 2. These results show that much higher depositionrates were generally obtained at a given temperature using trisilane, ascompared to silane, even when the flow rate for trisilane was lower thanthat for silane.

TABLE 2 Flow Set Deposition Temp. Pressure Point Rate No. (° C.) (Torr)(sccm) Precursor Substrate (Å/min.)  5C 650 40 50 SiH₄ SiO₂ 46  6C 65040 50 SiH₄ Si<100> 68  7 650 40 50 Si₃H₈ Si<100> 462  8C 600 40 50 SiH₄SiO₂ 19  9C 600 40 50 SiH₄ Si<100> 9 10 600 40 20 Si₃H₈ SiO₂ 359 11 60040 15 Si₃H₈ Si<100> 181 12C 550 760 25 SiH₄ SiO₂ <1 13C 550 40 50 SiH₄SiO₂ 7 14 550 40 30 Si₃H₈ SiO₂ 287 15C 550 40 50 SiH₄ SiO₂ 2

Examples 16-19

Si-containing films were deposited using trisilane and silane aschemical precursors, according to the parameters shown in Table 3.Deposition times were adjusted so that the films each had an averagethickness of about 500 Å. Deposition rates were determined by measuringaverage film thickness using a Nanometrics ellipsometer and thendividing this number by the deposition time. Film non-uniformity wasdetermined from a 49-point thickness map of the film thickness. Theresults show that a much more uniform film was obtained at a much higherdeposition rate by using trisilane at the indicated temperature in placeof silane. This is true at 550° C., but dramatically more so at 600° C.

TABLE 3 Deposition Rate No. Precursor Temp. (° C.) % Non-Uniformity(Å/min.) 16C SiH₄ 600 5.93 18.6 17 Si₃H₈ 600 0.83 372 18C SiH₄ 550 8.57.4 19 Si₃H₈ 550 7.31 287

Examples 20-38

Examples 1-19 are repeated except that SiGe films are obtained by usinga mixture of 80% trisilane and 20% digermane in place of trisilanealone, and by using a mixture of 80% silane and 20% germane in place ofsilane. Higher deposition rates were observed than with the use oftrisilane or silane alone.

Example 39

A SiGe film is prepared by superlattice growth with discontinuousperiodicity as follows, with reference to the flow chart shown in FIG.3. A Si <100> substrate is prepared 300 by performing an ex-situhydrogen-fluoride (HF) last clean to remove the native oxide layer,followed by introducing the substrate into a reactor chamber under ahigh flow of ultra-pure hydrogen gas. The wafer is rotated at 60 rpmwhile the wafer is heated to about 900° C. under a high flow of hydrogengas (to remove any contaminants from the substrate surface). The waferis cooled and allowed to stabilize at 700° C. and an arsenic-dopedsilicon buffer layer about 300 Å thick is grown using trisilane andtrisilylarsine under mass transport limited conditions.

The wafer temperature is adjusted 310 by cooling under hydrogen flow to600° C. The first period of SiGe superlattice is grown 320 using 98%disilane and 2% digermane. A second period of SiGe superlattice is grown330 using 85% trisilane and 15% digermane.

Under a flow of hydrogen, the set point temperature is lowered 340 by 3°C. and the wafer is allowed to stabilize for 30 seconds. A third periodof SiGe superlattice is grown 350 using 75% trisilane and 25% digermane.

Under a flow of hydrogen, the set point temperature is lowered 350 by 3°C. and the wafer is allowed to stabilize for 30 seconds. A fourth periodof SiGe superlattice is grown 370 using 65% trisilane and 35% digermane.A fifth period of SiGe superlattice doped with carbon and boron is grown380 using 85% trisilane, 12% digermane, 2% diborane and 1%disilylmethane. Under a flow of hydrogen, the reactor is purged 390 for30 seconds. A sixth period of SiGe superlattice is grown 400 using 90%trisilane and 10% digermane.

Under a flow of hydrogen, the temperature set point is increased 410 to650° C. and the relative powers of the lamp banks are adjusted slightlyto maximize the within-wafer uniformity of the silicon cap layer to begrown 420. The wafer is allowed to stabilize for 30 seconds. The siliconcap layer is grown using 100% trisilane. The wafer is removed 430 fromthe reactor and next wafer is processed.

Example 40

A Si-containing film having a mean thickness of 1,038 Å was depositedusing trisilane and germane as chemical precursors at a depositiontemperature of 650° C. and a pressure of 40 torr. The set points for gasflow injectors had been empirically tuned in the usual manner in aseries of previous runs. The resulting SiGe film had a thicknessnon-uniformity of 0.37% (range of 8 Å) as measured by a 49 point lineardimension scan with 6 mm edge exclusion. FIG. 4 is a plot of filmthickness as a function of measurement site for this film.

Example 41 Comparative

A Si-containing film was deposited onto a SiO₂ substrate (without anucleation layer) at a temperature of 600° C. using silane and germaneas precursors. The surface roughness of the resulting SiGe film (asmeasured by atomic force microscopy) was 226 Å for a 10 micron×10 micronscan area. Scanning electron microscopy (SEM) of the SiGe film revealedpyramidal, faceted grains indicative of an island-type deposition, asdemonstrated in the SEM micrographs shown in FIGS. 5 and 6.

Example 42

A Si-containing film was deposited at 600° C. as described in Example41, but trisilane and germane was used in place of silane and germane asprecursors. The surface roughness of the resulting SiGe film (asmeasured by atomic force microscopy) was 18.4 Å for a 10 micron×10micron scan area. SEM of the SiGe film revealed a much more uniformsurface, as demonstrated in the SEM micrographs shown in FIGS. 7 and 8(same magnifications and tilt angles as FIGS. 5 and 6, respectively).

Examples 43-63

A series of Si-containing films were deposited onto a SiO₂ substrate(without a nucleation layer) at a pressure of 40 torr using trisilaneand germane. The trisilane flow rate was constant at 77 sccm (hydrogencarrier, bubbler) for the examples of Table 4. Germane flow (10%germane, 90% H₂) and deposition temperature were varied as shown inTable 4. Germanium concentration (atomic %) and thickness of theresulting SiGe films were determined by RBS, and surface roughness wasdetermined by atomic force microscopy (AFM). The results shown in Table4 demonstrate that highly uniform films can be prepared over a range oftemperatures and flow rate conditions, particularly over a range ofgermane concentration.

TABLE 4 Germane Temp. Flow Thickness Deposition Roughness No. (° C.)(sccm) % Ge (Å) Rate (Å/min) (Å) 43 450 25 5.0  34* 8.5 3.2 44 450 507.5  34* 11 4.1 45 450 100 11  59* 15 3.7 46 450 100 11  53* 13 nd 47500 25 6.0 190 63 7.8 48 500 50 10 230 77 9.1 49 500 100 13.5 290 97 8.350 500 100 13.5  380* 127 7.2 51 550 25 6.0 630 315 5.2 52 550 50 9.5670 335 13.6 53 550 100 14 900 450 12.1 54 550 100 14 1016  508 9.4 55600 25 7.0 1160  580 8.1 56 600 50 13 1230  615 25.7 57 600 100 19 1685 843 31.8 58 650 25 11 630 630 23.3 59 650 50 17 800 800 31.5 60 650 10027 1050  1050 50.2 61 700 25 11 680 680 18.1 62 700 50 18 835 835 37.863 700 100 31 960 960 44.9 *Thickness measured by optical technique nd:not determined

Examples 64-78

A series of Si-containing films were deposited on the native oxide of Si<100> substrates under the conditions shown in Table 5 using trisilaneand ammonia (Examples 64-77) or silane and ammonia (comparative Example78). The carrier gas flow was 30 slm and the ammonia flow rate was 7slm. Table 5 shows the observed deposition rates and refractive indices(“RI”) for the resulting SiN films, as well as the atomic ratio ofsilicon to nitrogen (“Si/N”) and the hydrogen content (“% H”, atomicpercent) of selected films.

TABLE 5 Pressure Temp. Silicon source/ Deposition No. (Torr) (° C.)Carrier flow rate (sccm) Rate, Å/min. Si/N % H RI 64 20 675 N₂Trisilane/20 124 0.88 4 2.074 65 20 725 N₂ Trisilane/20 149 0.85 4 2.03466 20 725 N₂ Trisilane/80 585 0.95 4 2.182 67 20 725 H₂ Trisilane/80 6111.0 2.2 2.266 68 20 775 N₂ Trisilane/20 158 0.88 4 2.010 69 20 775 H₂Trisilane/20 117 0.88 3 1.999 70 20 775 N₂ Trisilane/40 308 0.85 4 2.05371 20 775 N₂ Trisilane/80 582 0.88 4 2.101 72 20 775 H₂ Trisilane/80 6000.88 3.5 2.146 73 20 775 N₂ Trisilane/160 1050 0.88 4 2.141 74 20 775 H₂Trisilane/160 1283 0.92 3.5 2.281 75 20 775 N₂ Trisilane/80 346 nd nd2.006 76 100 775 N₂ Trisilane/160 589 nd nd 2.028 77 100 775 H₂Trisilane/160 244 nd nd 2.012 78 100 775 N₂ Silane/40 208 nd nd 2.007nd: not determined

The values for Si/N and % H were determined by Rutherford Backscattering(RBS). FIG. 19 is a representative RBS spectrum (2 MeV He⁺⁺) of asilicon nitride sample deposited using trisilane at 775° C. and 20 Torr.An ERD spectrum obtained using Elastic Recoil Detection (ERD) is shownin FIG. 20. These Figures show both the raw data and simulations basedon the RUMP modeling program that enable quantification of the silicon,nitrogen, and hydrogen concentrations. The simulations indicate that thefilm has a stoichiometry of about Si₄₅N₅₁H₄. The RBS ERD spectrum shownin FIG. 17 also reveals that the hydrogen is distributed uniformlythroughout the film.

Example 79-82

A series of Si-containing materials were deposited onto the native oxideof Si <100> substrates using trisilane and atomic nitrogen. Atomicnitrogen was generated remotely using a commercially available 800 wattmicrowave radical generator (MRG) and was supplied to the CVD chamber.Trisilane was supplied to the CVD chamber along with the atomic nitrogenvia a bubbler using a nitrogen carrier gas at a flow rate of 5 slm (10slm for Example 82), at the deposition temperatures shown in Table 6.Trisilane was introduced to the chamber either continuously (Example 79)or in pulses (Examples 80-82). Pulsed introduction was accomplished bycontinuously introducing atomic nitrogen, and introducing trilisane inpulses at intervals of about 1 minute and 30 seconds. Each of thetrisilane pulses lasted about 6 seconds, under the flow conditionsdescribed above. Each of the resulting SiN films had a stoichiometry inthe range of approximately Si₄₃N₅₄₋₅₆H₃₋₁.

Table 6 shows the thicknesses, refractive indices and hydrogen levels(atomic %) in the resulting SiN films. The SiN film of Example 79 wasnot uniform because it was significantly thicker at the center than theedge, and the measured refractive index varied significantly across thesurface of the film (higher at center than edge). Uniformity wasimproved by using the pulsed processes of Examples 80-82. Uniform filmscan also be obtained using the continuous process by increasing the flowrate of atomic nitrogen and/or decreasing the flow rate of trisilane.

TABLE 6 Film Deposition Thickness (Å) Refractive No. Process Temp. (°C.) Center Edge Index % H 79 Continuous 650 869 510 1.97-2.2 2 80 Pulsed650 324 268 1.98 2 81 Pulsed 600 635 655 1.96 3 82 Pulsed 650 1115 11742.02 0.7

Example 83

A thin, uniform, continuous SiN film having a thickness of about 18 Åwas deposited at 650° C. at a pressure of 3 torr using remotelygenerated atomic nitrogen and a single six-second pulse of trisilane, asgenerally described above for Examples 80-82. The film was coated withepoxy, cross-sectioned and imaged using transmission electron microscopy(TEM), as shown in the TEM photomicrograph of FIG. 9. The film/substrateinterface was found to be essentially free of native oxide.

Examples 84-87

A series of epitaxial silicon films were deposited onto cleaned Si <100>substrates using trisilane at a deposition pressure of 40 Torr andvarious flow rates, and at the deposition temperatures and depositionrates shown in Table 7. High quality epitaxial silicon films wereproduced, as indicated by the χ-min values obtained from RutherfordBackscattering channeling spectra as shown in Table 7.

TABLE 7 Deposition Deposition No. Temperature (° C.) Rate (Å/min) χ-min(%) 84 550 47 2.7 85 600 50 3.1 86 600 145 2.9 87 650 460 3.2

It will be appreciated by those skilled in the art that variousomissions, additions and modifications may be made to the processesdescribed above without departing from the scope of the invention, andall such modifications and changes are intended to fall within the scopeof the invention, as defined by the appended claims.

1. A process for depositing a Si-containing material on a surface,comprising: providing a chemical vapor deposition chamber havingdisposed therein a substrate, wherein the chemical vapor depositionchamber is a single-wafer, horizontal gas flow reactor; introducing agas comprising trisilane to the chamber at a partial pressure in therange of about 1×10⁻⁴% to about 100% of total pressure in the chamber,and at a flow rate selected to improve deposition rate and filmuniformity; and depositing a Si-containing film onto the substrate at atemperature higher than 525° C., the film having a greater degree ofthickness uniformity and being deposited at a substantially higherdeposition rate than a comparable film made by a substantially identicalprocess under substantially identical conditions but using silane inplace of the trisilane; wherein the Si-containing film has a thicknessnon-uniformity of about 5% or less and is deposited at a deposition rateof about 50 Å per minute or higher.
 2. The process as claimed in claim1, wherein the substrate is maintained at a temperature of about 550° C.or higher.
 3. The process as claimed in claim 1, wherein the substrateis maintained at a temperature of about 620° C. or higher.
 4. Theprocess as claimed in claim 1, wherein the chamber is maintained at atotal pressure between about 1 Torr and 60 Torr.
 5. The process of claim4 in which the Si-containing film is conformal.
 6. The process asclaimed in claim 1, wherein the substrate is maintained at a temperaturein the range of 525° C. to about 700° C.
 7. The process as claimed inclaim 1, wherein the substrate is maintained at a temperature in therange of about 525° C. to about 650° C.
 8. The process as claimed inclaim 1, wherein the deposition is carried out at a rate of about 100 Åper minute or higher.
 9. The process as claimed in claim 1, wherein thegas further comprises one or more compounds selected from the groupconsisting of germane, digermane, trigermane, NF₃, monosilylmethane,disilylmethane, trisilylmethane, tetrasilylmethane, a carbon source, anda dopant precursor.
 10. The process as claimed in claim 1, wherein thegas further comprises digermane.
 11. The process as claimed in claim 1,wherein the Si-containing film has a thickness non-uniformity of about1% or less.
 12. The process as claimed in claim 1, wherein theSi-containing film is selected from the group consisting of a microdot,a SiGe film, a SiGeC film, a SiN film, a SiC film, a SiOC film, a SiNCfilm, a silicon-oxygen film, a silicon-oxygen-nitrogen film, aboron-doped film, an arsenic-doped film, an indium-doped film, anantimony-doped film, a phosphorous-doped film, and a film having adielectric constant of about 2.2 or lower.
 13. The process as claimed inclaim 1, wherein the Si-containing film is silicon and the substrate isa material having a high dielectric constant.
 14. The process as claimedin claim 1, wherein the Si-containing film is epitaxial.
 15. The processas claimed in claim 1, wherein the Si-containing film ispolycrystalline.
 16. The process as claimed in claim 1, wherein theSi-containing film is amorphous.
 17. The process as claimed in claim 1,further comprising patterning to form a transistor gate electrode. 18.The process of claim 1 in which the gas further comprises a carbonsource.
 19. The process of claim 18 in which the Si-containing film hasa carbon content of about 20% or less.
 20. The process of claim 18 inwhich the Si-containing film is selected from the group consisting of aSiGeC film, a SiC film, a SiOC film, and a SiNC film.
 21. The process ofclaim 20 in which the substrate is a single-crystal substrate.
 22. Theprocess of claim 21 in which the Si-containing film is heteroepitaxial.23. The process of claim 18 in which the chamber is a single-wafer,horizontal gas flow reactor.
 24. The process of claim 18 in which thecarbon source is selected from the group consisting of a silylmethane, ahydrocarbon, carbon monoxide, carbon dioxide and HCN.
 25. The process ofclaim 18 in which the deposition of the Si-containing film is conductedat a chamber pressure in the range of about 0.1 Torr to about 200 Torr.26. The process of claim 25 in which the SiGe film is conformal.
 27. Theprocess of claim 18 in which the deposition of the Si-containing film isconducted at a substrate temperature in the range of about 450° C. toabout 700° C.
 28. A process for depositing a SiGe material on a surface,comprising: providing a chemical vapor deposition chamber havingdisposed therein a substrate, wherein the chemical vapor depositionchamber is a single-wafer, horizontal gas flow reactor, introducing agas comprised of a higher-order silane of the formula Si_(m)H_(2m+2),where m=2-6, and a higher-order germane of the formula Ge_(n)H_(2n+2),lwhere n=2-4, to the chamber at a partial pressure in the range of about1×10⁻⁴% to about 100% of total pressure in the chamber, and at a flowrate selected to improve deposition rate and film uniformity; anddepositing a SiGe film onto the substrate, wherein the SiGe film hasgreater thickness uniformity than a comparable film made by asubstantially identical process under substantially identical conditionsbut using silane in place of the higher-order silane; wherein the SiGefilm has a thickness non-uniformity of about 5% or less and is depositedat a deposition rate of about 50 Å per minute or higher.
 29. The processas claimed in claim 28, wherein the higher-order silane is selected fromthe group consisting of disilane, trisilane, and tetrasilane.
 30. Theprocess as claimed in claim 28, wherein the higher-order silane istrisilane and the higher-order germane is digermane.
 31. The process asclaimed in claim 28, wherein the depositing is carried out at atemperature in the range of 475° C. to about 700° C.
 32. The process asclaimed in claim 28, wherein the depositing is carried out at a rate ofabout 100 Å per minute or higher.
 33. The process as claimed in claim28, wherein the gas further comprises one or more compounds selectedfrom the group consisting of monosilylmethane, disilylmethane,trisilylmethane, tetrasilylmethane, and a dopant precursor.
 34. Theprocess as claimed in claim 28, wherein the SiGe film has greaterthickness uniformity than a comparable film made by a substantiallyidentical process under substantially identical conditions but usinggermane in place of the higher-order germane.
 35. The process as claimedin claim 28, further comprising patterning to form a transistor gateelectrode.
 36. A process for depositing a Si-containing material on asurface, comprising: providing a chemical vapor deposition chamberhaving disposed therein a substrate, wherein the chemical vapordeposition chamber is a single-wafer, horizontal gas flow reactor;introducing a gas comprising trisilane and a carbon source to thechamber at partial pressures in the range of about 1×10⁻⁴% to about 100%of total pressure in the chamber, and at flow rates selected to improvedeposition rate and film uniformity; and depositing a Si-containing filmonto the substrate, the film comprising carbon, wherein theSi-containing film has greater thickness uniformity than a comparablefilm made by a substantially identical process under substantiallyidentical conditions but using silane in place of the trisilane; whereinthe Si-containing film has a thickness non-uniformity of about 5% orless and is deposited at a deposition rate of about 50 Å per minute orhigher.
 37. The process of claim 36 in which the Si-containing film hasa carbon content of about 20% or less.
 38. The process of claim 36 inwhich the Si-containing film is selected from the group consisting of aSiGeC film, a SiC film, a SiOC film, and a SiNC film.
 39. The process ofclaim 36 in which the substrate is a single-crystal substrate.
 40. Theprocess of claim 39 in which the Si-containing film is heteroepitaxial.41. The process of claim 36 in which the Si-containing film is depositedonto the substrate under substantially mass transport limitedconditions.
 42. The process of claim 36 in which the carbon source isselected from the group consisting of a silylmethane, a hydrocarbon,carbon monoxide, carbon dioxide and HCN.
 43. The process of claim 36 inwhich the deposition of the Si-containing film is conducted at a chamberpressure in the range of about 0.1 Torr to about 200 Torr.
 44. Theprocess of claim 36 in which the deposition of the Si-containing film isconducted at a substrate temperature in the range of about 450° C. toabout 700° C.
 45. The process of claim 43 in which the Si-containingfilm is conformal.
 46. The process of claim 36 in which the carbonsource in the chamber has a partial pressure of about 1% or less.